The present invention relates to cemented carbide bodies useful in tools for rock drilling and mineral cutting. Tools for cutting asphalt and concrete are also included.
In U.S. Pat. No. 4,743,515 cemented carbide bodies are disclosed with a core of fine and evenly distributed eta-phase embedded in the normal alpha+beta-phase structure, and a surrounding surface zone of only alpha+beta-phase. (Alpha=tungsten carbide, beta =binder phase, e.g., Co, and eta=M.sub.6 C, M.sub.12 C and other carbides, e.g., W.sub.3 Co.sub.3 C). An additional condition is that in the inner part of the surface zone situated close to the core, the Co-content is higher than the nominal content of Co (with nominal is meant here and henceforth the weighed-in amount of Co). In addition, the Co-content in the outermost part of the surface zone is lower than the nominal and increases in the direction towards the core up to a maximum situated in the zone free of eta-phase. The zones free of eta-phase may, e.g., be created by adding carbon at high temperature to the surface zone of a body with eta-phase throughout.
Cemented carbide bodies, according to U.S. Pat. No. 4,743,515 have shown increased performance for all cemented carbide grades normally used in rock drilling and have been a commercial success. Because the binder phase content increases from the outer surface towards the center, the improved wear resistance is lost relatively early in the drilling process. Cemented carbide bodies according to U.S. Pat. No. 4,743,515 are therefore best suited for rock drilling operations demanding toughness in the bits.
High wear resistance and high penetration rate are essential properties for bits and these properties are becoming more and more important. Certain bits, in particular bits for drifting, are worn out when the diameter of the bit has decreased with 4-6 mm since the diameter of the drill hole becomes too small, thus making the blasting agent difficult to charge. Buttons in such bits are therefore seldom reground because the bit diameter usually decreases when reground. For these bits, it is important that the buttons have a 2-3 mm thick, wear resistant zone so that the wear resistance is high and uniform during the whole life of the bit. The penetration rate depends on the shape of the button. The buttons are therefore as a rule given a shape which give optimal penetration rate. When the shape of the button is changed by wear, the penetration rate decreases successively.